Electronic thermometers are widely used in the healthcare field for measuring a patient's body temperature. Typical electronic thermometers have a base unit that is held in the palm of a hand and a probe with an elongated shaft connected to the base. The base unit includes a probe well for holding the probe when the thermometer is not in use. Electronic temperature sensors such as thermistors or other temperature sensitive elements are contained within a tip of the probe. When the tip is placed, for example, in a patient's mouth, the tip is heated up by the patient's body and the thermistor measures the temperature of the tip. Electronic components in the base unit receive input from the sensor components to compute the patient's temperature. The temperature is then typically displayed on a visual output device such as a seven segment numerical display device. Typically, electronic thermometers are powered by batteries to make the thermometers portable. Since the thermometers are portable, wall mounts or other holders may be included with the thermometers to provide places to securely store the thermometers.
Electronic thermometers also typically include an automatic on/off mechanism to conserve power consumption of the batteries. One type of on/off mechanism employs an on/off switch configured so that when the probe is placed in the probe well of the base unit, the thermometer automatically powers off, and when the probe is removed from the base unit, the thermometer automatically powers on. A conventional on/off switch may include a true mechanical switch. The mechanical switch is part of a power circuit, whereby when the switch is open, the thermometer is off, and when the switch is closed, the thermometer is on. The switch is located within the base unit of the thermometer and comprises a lever arm that is biased in a first position, whereby the switch is closed. When the probe is inserted into the base unit, the probe contacts the lever arm and pivots the arm to a second position in which the switch opens and power is shut off from the thermometer. Because the true mechanical switch involves several moving, mechanical parts, the switch is prone to wear and failure.
Yet another type of on/off switch includes an optical switch. The thermometer includes a light emitter, such as an LED, that emits an infrared light beam that passes across a probe well. When the probe is inserted into the probe well, the light beam is blocked and the light detector cannot sense the light. This causes a signal to be sent to a microcontroller to turn the thermometer off. When the probe is removed, the light beam passes across the probe well and is detected by the light detector, which creates a signal to the microcontroller to turn the thermometer on. A disadvantage with the optical switch is debris in the probe well blocking the light emitter or the light detector and interfering with the ability of the detector to sense the light from the light emitter when the probe is removed from the probe well. Moreover, humidity may negatively affect the ability of the light detector to sense the light from the light emitter. The optical switch is also complex and costly to assembly, in part because the light emitter and the light detector must be properly aligned in the thermometer. Further still, the optical switch consumes substantial battery power.